Perfluoroalkanes refer to a specific group of halogen-containing compounds that are composed of only carbon and fluorine atoms and do not possess double or triple bonds. Perfluoroalkanes differ from, for example, chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's) and hydrofluorocarbons (HFC's) in that perfluoroalkanes do not contain hydrogen, chlorine or heteroatoms other than fluorine. Perfluoroalkanes are released to the environment during certain industrial processes, such as electrolytic aluminum smelting for example, as by-products during the manufacture of tetrafluoroethylene, and during semiconductor manufacturing processes. Examples of perfluoroalkanes include carbon tetrafluoride (CF.sub.4), hexafluoroethane (C.sub.2 F.sub.6), octafluoropropane (C.sub.3 F.sub.8), octafluorocyclobutane (C.sub.4 F.sub.8) and decafluoroisobutane (C.sub.4 F.sub.10). Perfluoroalkanes represent some of the most stable compounds known (Kiplinger et al. Chem. Rev. p. 373 (1994). The stability of perfluoroalkanes makes these compounds difficult to decompose or convert to useful products, such as for example the conversion of perfluoroalkanes to perfluoroalkenes. Also, this highly stable characteristic make perfluoroalkanes released into the atmosphere undesirable because of their contribution to global warming effects.
A number of catalysts and catalytic processes have been reported for the decomposition of halogen-containing organic compounds. A review of the literature reveals that the majority of these catalysts and catalytic processes focus on the decomposition of chlorine-containing compounds, or the destruction of organic compounds which contain only chlorine and fluorine. Bond and Sadeghi, in an article entitled "Catalyzed Destruction of Chlorinated Hydrocarbons", J. Appl. Chem. Biotechnol, p. 241 (1975), report the destruction of chlorinated hydrocarbons over a platinum catalyst supported on high surface area alumina.
Karmaker and Green, in an article entitled "An investigation of CFC12 (Ccl.sub.2 F.sub.2) decomposition on TiO.sub.2 Catalyst," J. Catal, p. 394 (1995), report the use of a TiO.sub.2 catalyst to destroy CFC12 at reaction temperatures between 200 and 400.degree. C. in streams of humid air.
Bickel et al, in an article entitled "Catalytic Destruction of Chlorofluorocarbons and Toxic Chlorinated Hydrocarbons", Appl. Catal B:Env. p. 141 (1994), report the use of a platinum catalyst supported on phosphate-doped zirconium oxide for the destruction of CFC113 (Cl.sub.2 FCCClF.sub.2) in air streams. The catalyst was able to achieve greater than 95% destruction of CFC113 at reaction temperature of 500.degree. C. for approximately 300 hours of continuous operation.
Fan and Yates, in an article entitled "Infrared Study of the Oxidation of Hexafluoropropene on TiO.sub.2," J. Phys. Chem., p. 1061 (1994), report the destruction of a perfluoroalkene over TiO.sub.2. Perfluoroalkenes differ from perfluoroalkanes in that they contain a carbon-carbon double bond. Although the catalyst was able to readily destroy hexafluoropropylene (C.sub.3 F.sub.6), the loss of titanium, as TiF.sub.4. was evident. The formation of TiF.sub.4 would undoubtedly lead to deactivation of the catalyst.
Farris et al, in an article entitled "Deactivation of a Pt/Al.sub.2 O.sub.3 Catalyst During the Oxidation of Hexafluoropropylene," Catal. Today, p. 501 (1992), report the destruction of hexafluoropropylene over a platinum catalyst supported on a high surface area alumina carrier. Although the catalyst could readily destroy hexafluoropropylene at reaction temperatures between 300 and 400.degree. C., deactivation of the catalyst, resulting from the transformation of aluminum oxide to aluminum trifluoride, was severe.
Campbell and Rossin, in a paper entitled "Catalytic Oxidation of Perfluorocyclobutene over a Pt/TiO.sub.2 Catalyst," presented at the 14th N. Am. Catal. Soc. Meeting (1995), reported the use of a platinum catalyst supported on high surface area TiO.sub.2 carrier to destroy perfluorocyclobutene (C.sub.4 F.sub.6) at reaction temperatures between 320 and 410.degree. C. The authors note than even at a reaction temperature of 550.degree. C., no conversion of perfluorocyclobutane (C.sub.4 F.sub.8), a perfluoroalkane, could be achieved using the Pt/TiO.sub.2 catalyst. Results presented in this study demonstrate that perfluoroalkanes are significantly more difficult to transform than perfluoroalkenes.
Nagata et al, in a paper entitled "Catalytic Oxidative Decomposition of Chlorofluorocarbons (CFC's) in the Presence of Hydrocarbons", Appl. Catal. B:Env., p. 23 (1994), report the destruction of 1,1,2-trichloro 1,2,2-trifluoroethane (CFC113), 1,2 dichloro 1,1,2,2-tetrafluoroethane (CFC114) and chloropentafluoroethane (CFC115) in the presence of hydrocarbons using a .gamma.-alumina catalyst impregnated with vanadium, molybdenum, tungsten and platinum. The decomposition of the CFC's became more difficult as the number of carbon atoms in the CFC molecule decreased. However, results indicate that as the number of chlorine atoms in the molecule are decreased by replacement with fluorine, the compounds become increasingly more difficult to decompose.
Burdeniue and Crabtree, in an article entitled "Mineralization of Chlorofluorocarbons and Aromatization of Saturated Fluorocarbons by a Convenient Thermal Process", Science, p. 340 (1996), report the transformation of cyclic perfluoroalkanes to perfluoroarenes via contact with sodium oxalate to yield sodium fluoride as a reaction product. Both reactions, however, are slow and non-catalytic, since sodium oxalate is stoichiometrically consumed (via transformation into NaF) during the course of the reaction. This process would not be able to destroy perfluoroalkanes present in streams of air, since the oxygen and/or moisture in the air would readily convert the sodium oxalate to sodium oxide.